1. Field of the Invention
The present invention relates to heat insulation walls requiring heat insulation in a heat insulation box body such as a refrigerator, or the like, in which wall surfaces are formed of thin metal plates, resin moldings, or the like. More particularly, the present invention relates to a full vacuum heat insulation box body in which porous structural materials are disposed in a shell constituting heat insulation walls for the purpose of preventing deformation so that a vacuum is kept, a refrigerator using such a full vacuum heat insulation box body, a method for producing such a full vacuum heat insulation box body, and a method for disassembling such a full vacuum heat insulation box body.
2. Description of the Related Art
Conventionally, a shell of a refrigerator, or the like, is so constituted that an outer box is formed of a thin metal plate such as an iron plate, an inner box is formed of a resin molding, and closed-cell foaming urethane used for forming a structural material, is injected into a gap between the inner and outer boxes and foamed so that the gap is filled with the structural material.
FIG. 16 is a flow chart illustrating a process of producing a conventional refrigerator using closed-cell foaming urethane as a heat insulating material in walls, and FIG. 17 illustrates a foaming urethane injection step in the process.
That is, in a conventional refrigerator, or the like, an inner box 2 obtained by attaching necessary members, such as an anchor for fixing interior parts, piping for supplying a refrigerant, etc., to a vacuum molding of an ABS resin sheet, is inserted in an outer box 1 of a formed product obtained by bending a steel plate to thereby form a shell. Injection portions 4 are provided in the outer box 1 (step 1 ) to inject a mixture solution 3 of foaming urethane.
After sheet metal worked parts are attached to the back and bottom portions which are residual opening portions, a slight gap in each engaging portion is sealed with a hot melt adhesive agent, or the like, and further interior parts are partially assembled (step 2).
The thus obtained box body is laid down as shown in FIG. 17, and fixed in a foaming jig heated to an arbitrary temperature. After a mixing head 5 is successively inserted into and fixed to injection holes of the injection portions 4 provided in the outer box 1, a mixture solution 3 of foaming urethane is discharged and injected. Then, injection portions 4 are sealed with plugs. Because the foaming urethane mixture solution 3, at the time of injection, is a liquid having an expansion ratio in a range from several times to tens of times, the mixture solution 3 flows in a flange portion corresponding to the opening portions of the box body through the injection portion 4 so as to disperse. Further, after some seconds, a foaming agent is vaporized by reaction heat of raw materials and thereby the foam is caused to fill the residual gap between the inner box 2 and the outer box 1 with urethane foam. A heat insulation box body thus formed can be taken out from the foaming jig after some minutes, generally about 5 minutes from the injection (step 3).
Residual parts, for example, electric parts such as a fan motor and a light and interior parts such as shelves and various kinds of casings are put in the thus obtained heat insulation box body. After refrigerant circuit securing parts for securing a refrigerant circuit are attached to the heat insulation box body, the refrigerant circuit is charged with a refrigerant. Thus, assembling of the product is completed (step 4).
Inspection of various kinds of functions of the completed product is carried out through an actual operation so as to confirm that the product is not defective (step 5).
When a package and documents pertinent to the obtained product are prepared and added, the production is completed (step 6).
It has been found that the chlorine containing 1,1-dichloro-1-fluoroethane (HFC141b), which is one of hydrochlorofluorocarbons that has been used as a foaming agent for forming urethane foam used as a heat insulating material herein, is a cause of ozone layer destruction. Accordingly, use of hydrofluorocarbons or hydrocarbons which do not contain chlorine in their molecules, has been proposed in recent years.
For example, a method for producing urethane foam by use of hydrofluorocarbons such as 1,1,1,3,3-pentafluoropropane (HFC245fa) and 1,1,1,4,4,4-hexafluorobutane (HFC356mffm) as a foaming agent is disclosed in JP-A-2-235982, and a method for producing urethane foam by use of hydrocarbon such as cyclopentane, or the like, as a foaming agent is disclosed in JP-A-3-152160.
However, the heat insulating property of such urethane foam is in a range from 19 to 20 mw/MK and clearly inferior to the heat insulating property of 16 mw/MK of chlorofluorocarbons used before issue of regulations on use of ozone layer destruction substances.
Since the improvement of the heat insulating property of urethane foam has reached a limit, a technique of applying a vacuum heat insulation panel which has more than twice as higher heat insulating property as the urethane foam as shown in the comparison view of FIG. 18 has been proposed for a refrigerator, or the like, allowing a reduction of electric power consumption without use of any substance which causes ozone layer destruction.
For example, JP-A-60-243471 discloses a heat insulation box body in which a member obtained by putting pulverized PUF in a synthetic resin bag and vacuum-packing the pulverized PUF in the form of a board is disposed inside walls, and JP-A-60-60483 proposes a refrigerator in which a vacuum heat insulation panel having a gap which is provided in the flange side of a side plate to allow PUF to flow in the gap is disposed in a side wall of the refrigerator.
The vacuum heat insulation panel such as those proposed above, has a structure shown in FIG. 19. A method for producing the vacuum heat insulation panel will be described below. First, a core material 11 having a porous structure such as an aggregate of fibers or particles, a foam having open cells, or the like, is inserted into a bag-like packing material 12. Then, in order to generate a high quality heat insulating property, its inside is deaerated by using a vacuum panel making machine 15 comprising fusion-bonding devices 17 each having a heater 17a, sealing pressure devices 18, and a vacuum control valve 16 as shown in FIG. 20. While a vacuum state is maintained, end edge portions 12a of the packing material 12 containing the core material 11 are heat-sealed to prevent external air from entering inside. Thus, a vacuum heat insulation panel 13 shown in FIG. 19 is obtained. Preferably, the inside of the vacuum panel making machine 15 is kept to 10xe2x88x922 torr when the end edge portions 12a are subjected to fusion bonding. Therefore, adjustment of the degree of vacuum is performed by use of the vacuum control valve 16 connected to an evacuator not shown.
Accordingly, in the packing material 12, a thin metal film layer is used as its intermediate layer for blocking or suppressing entrance of gas from the outside into the vacuum heat insulation panel to thereby keep a heat insulating property. A material having excellent welding property is used as its inner layer so that insertion openings can be sealed perfectly, and a material for stably securing adhesion to urethane foam is used as its surface layer so that generation of scratches is suppressed and bending strength of walls in a box body such as a refrigerator, or the like, can be secured. Because the packing material 12 is required to have various characteristics as described above, a multilayer sheet in which different materials are laminated to satisfy the required characteristics is used.
Further, the core material 11 must have a strength higher than atmospheric pressure to satisfy a function of holding the panel shape in a vacuum state and the quantities of conducted heat (heat conduction) and penetrated heat (heat radiation) through a substance constituting the core material itself must be suppressed to thereby contribute to improvement of heat insulating property. Accordingly, a porous plate formed of a substance with small heat transfer rate is used as the core material 11.
That is, in order to improve the heat insulating property of the vacuum heat insulating panel 13, it is important to use a substance that is a good insulator for the core material 11 among constituent materials, reduces the heat-conduction area of the material to suppress the heat conduction through the substance, and reduces the gap to suppress heat radiation. As a substance satisfying the aforementioned conditions, a porous material of resin, glass, or the like, is preferably used. In particular, a mat of glass fiber, a board of a resin foam having open cells, or a molding of resin or inorganic fine particles is used preferably.
For example, JP-A-60-71881 has proposed a material obtained by putting pearlite powder in a synthetic resin bag and vacuum-packing it into the form of a board. Similarly, JP-A-60-243471 has proposed a material obtained by putting pulverized PUF in a synthetic resin bag and vacuum-packing it into the form of a board. As other proposals, JP-A-60-205164 has proposed hard polyurethane foam having open cells, JP-A-4-218540 has proposed a plate-like molding which is formed from thermoplastic urethane resin powder firmly bonded and, JP-A-7-96580 has proposed a board which comprises long glass fiber, fibrillated resin fiber and inorganic fine powder, each of which is applied as a core material of the vacuum heat insulation panel.
Each of the vacuum heat insulation panels, such as those proposed above, is generally shaped as a board or a substrate having a thickness in a range from 10 to 20 mm and is typically incorporated into the wall of the refrigerator. That is, after the inner box is inserted into the outer box equipped with the vacuum heat insulation panels stuck thereon so that the inner box is united with the outer box, a raw material mixture solution of foaming urethane is injected thereto, foamed and molded to thereby form a heat insulation wall.
Accordingly, in the case of a refrigerator, the vacuum heat insulation panel is usually not stuck on the inner box having an uneven surface for shelf rests, or the like, but fixed to the outer box surface by use of an adhesive agent, or the like, so that foaming urethane to fill the gap in the shell containing the vacuum heat insulation panels disposed therein is fully packed without any remaining gap to thereby prevent spoilage of design characteristic such as deformation, or the like.
However, in the cases that the packing material has some fine defect which is larger than expected, a part of the packing material is destroyed by an external factor or a large amount of volatile substance remains in or sticks to the core material, thereby creating a number of possibilities that a desired heat insulating property cannot be provided.
As described above, in the heat insulation wall structure of the conventional heat insulation box body, the vacuum heat insulation panel is disposed in the shell and the residual space is filled with urethane foam having closed cells. Therefore, if the aforementioned failure occurs in the vacuum heat insulation panel, it is not only very difficult to repair the vacuum heat insulation panel but also impossible to replace the vacuum heat insulation panel with a new one. That is, the heat insulation wall is conventionally formed on the assumption that the whole of a system such as a heat insulation box body, a refrigerator, or the like, must be scrapped when the aforementioned failure occurs.
As a method to enable lowering of the degree of vacuum caused by the aforementioned possibilities to be repaired, there has been proposed a heat insulation box body having heat insulation walls in which all the inside of the shell of the heat insulation box body is set in a vacuum state. For example, JP-A-57-52783 has proposed to insert an air-permeable bag containing a powder substance into the gap between the inner and outer boxes, JP-A-3-140782 has proposed to put particles of pearlite, or the like, into the hollow resin shell, and JP-A-2-192580 and JP-A-7-148752 have proposed to inject foaming heat insulating material such as foaming urethane with open cells into the shell. Each of the shells is evacuated with a vacuum pump, or the like, through a gas exhaust hole provided in a part of the shell to secure the vacuum state inside the shell of the heat insulation box body.
In the conventional heat insulation box body configured so that all the heat insulation wall is kept in a vacuum state as described above, it has been found that it is very difficult to fill the inside of the shell with a powder or granular substance uniformly and densely when the powder or granular substance is put in the shell. Accordingly, if the inside of the shell is kept in a vacuum state, the shell is pressed by atmospheric pressure so as to be partly or wholly contracted, so that deterioration of design characteristic may be caused or in some cases, deterioration of heat insulating property caused by reduction of the wall thickness may be triggered.
Further, in filling a heat insulation box body having inferior filling property such as a large-size refrigerator, or the like, a larger amount of filling is required than the amount of filling to corresponding to the density for obtaining a strength required to prevent deformation caused by the atmospheric pressure.
Accordingly, there arise disadvantages such as economical loss, increase of weight, lowering of heat insulating property, etc.
Further, in filling the heat insulation box body with open-cell foaming urethane, communication of bubbles cannot be sufficiently achieved so that closed cells remain, if bubbles in a foamed state flow over a short distance from the start point of foaming, bubbles flow in a state of stable shape after completion of bubble growth, and so on.
Further, because foaming gas remaining in bubbles remains in cells or is adsorbed into a resin constituting cells even in a portion in which communication of cells is achieved, foaming gas remains. Accordingly, if this is used as it is, for a structural material, there arises a disadvantage that not only a long time is required for evacuation particularly of a large-size full vacuum heat insulation box body but also a degree of vacuum changes is lost over the passage of time.
That is, in accordance with the aforementioned proposals, it is indispensable to perform troublesome evacuation substantially periodically by use of a vacuum pump, or the like, or to incorporate a suction system for the purpose of preventing a drop in the degree of vacuum due to generation of gas in the shell. Furthermore, in a state where the inside of the shell is filled with no gap, a long evacuation time is required because this structure brings a great disadvantage for sucking remaining gas in an opposite portion inside the shell to the gas-exhaust hole up to all open cells through a long distance along open cells by use of a vacuum pump from a gas-exhaust hole provided in an end portion of the heat insulation box body such as a refrigerator, or the like, to thereby perform evacuation to secure a sufficient vacuum state. Further, during the period when the degree of vacuum drops with the passage of time, a cooling operation is carried out frequently, so that electric power is additionally consumed and the temperature of the inside of the refrigerator becomes unstable to cause a problem in that the freshness of foods is affected.
Further, when the full vacuum heat insulation box body obtained by the conventional production method is to be disassembled after scrapping so as to recycle parts or members, some measures are required to prevent scattering of the filling materials at the time of disassembling or collecting in the former case of filling powder or granular materials, and it is also difficult to handle the materials without damage even in the case of employing a method in which the filling materials are disposed in a form protected by bags, or the like.
On the other hand, in the latter case of the full vacuum heat insulation box body in which a raw-material mixture solution of foaming urethane is injected into the shell and foamed to thereby form heat insulation walls, the filled urethane foam firmly self-adheres to the inner and outer boxes constituting the shell so as to be nearly inseparable therefrom when the box body is to be disassembled after scrapping to recycle the members. In the conventional method therefore, the shell is not separated into constituent members but the inner and outer boxes and the filled urethane foam self-adhering thereto are collectively subjected to a crusher so as to be broken up, and then, the crushed parts are separated into respective members by use of a separation method using weight or magnetic characteristic arranged for a subsequent step to the crusher, so that the outer box is magnetically attached, the inner box is made to fall down by itself by weight and the urethane foam is flown off, for example, laterally by use of wind, or the like. It is however impossible to perfectly separate the urethane foam self-adhering to the inner and outer boxes from adhering surfaces. Accordingly, used members cannot be reused and therefore, recycling of the members is difficult using the conventional methods.
A technical object of the present invention is to entirely hold the inside of heat insulation walls in a vacuum state as well as to provide easy evacuation, light-weight and uniform strength, reduction of remaining gas and prevention of entrance of gas from the outside, and also to facilitate disassembling after scrapping of the heat insulation walls so as to simplify recycling of respective members.
In order to achieve the above object, according to one aspect of the present invention, a full vacuum heat insulation box body in which the inside of its heat insulation walls is filled with structural materials having continuous pores and kept in a vacuum state, is constructed such that inner and outer boxes constituting a shell of the heat insulation box body and the structural material put between the inner and outer boxes are held only by close-contact caused by means of a vacuum. With this configuration, the constituent materials of the box body can be separated and collected easily when disassembling the box body after scrapping, without leaving material on the abutting parts.
Preferably, the shell of the heat insulation box body has an uneven surface, and the structural materials abutting on the uneven surface of the shell include moldings formed of a pulverized resin foam. With this configuration, a non-filling portion is not produced between the uneven surface of, for example, the inner box and the abutting surface of the structural materials, so that flaws in design characteristic such as surface deformation can be prevented even in the case where the inside of the shell is kept in a vacuum.
Preferably, the structural materials contain parts comprising grooves or holes for exhausting air and continuous pores. With this configuration, gas such as air remaining in the shell can be exhausted easily, resulting in a short time required for evacuation and a high degree of vacuum secured to improve heat insulating property.
Preferably, the structural materials are constituted by a resin foam having open cells. With this configuration, heat insulation walls with small heat conduction can be formed, so that the quantity of leaking heat can be suppressed and heat insulating properties can be improved.
Preferably, the structural materials have parts each having a triangular section, each of the triangular-section parts being disposed in a middle layer in the direction of wall thickness, or in a layer abutting an even surface of the shell. With this configuration, a wedge effect is obtained so that the walls are never slackened or deformed, and an inferior design characteristic such as deformation can be prevented.
Preferably, the parts having a triangular section are formed of polystyrene foam having open cells. With this configuration, dust, or the like, is never produced even if surfaces of the parts are rubbed in handling, moderate flexibility necessary for handling is provided to improve working efficiency, and a strength tolerant to the atmospheric pressure and a fine cell shape are provided to provide both excellent external appearance and heat insulating property.
Preferably, the polystyrene foam having open cells has flattened cells which are spread in a direction perpendicular to the direction of wall thickness. With this configuration, the effect of blocking radiation heat in a heat-insulating direction are improved.
Preferably, a joint portion between the inner and outer boxes is constituted by a groove of a predetermined depth formed by bending one of the boxes and is filled with a liquid substance having an adhesive sealing function and an end side portion formed in the other box so as to be able to be inserted into a deep portion of the groove. Joining and sealing of the joint portion are performed by the liquid substance by utilizing mutual attraction force produced at the time of evacuation of the shell. With this configuration, the inner and outer boxes can operate as a piston. Structural materials can be pressed from the outside by the inner and outer boxes, so that the degree of close-contact between the structural materials can be enhanced on the basis of a vacuum.
Preferably, an opening portion, which is later closed with a plate member, for inserting the structural materials is provided in the outer box, a joint portion between the outer box and the plate member is constituted by a groove of a predetermined depth formed by bending one of the outer box and the plate member and filled with a liquid substance having an adhesive sealing function and an end side portion formed in the other of them so as to be able to be inserted into a deep portion of the groove. Joining and sealing of the joint portion are performed by the liquid substance by utilizing mutual attraction force produced at the time of evacuation of the shell. With this configuration, the plate member can operate as a piston. Structural materials disposed in the opening portion can be pressed from the back side by the plate member, so that the degree of close-contact between the structural materials can be enhanced on the basis of a vacuum.
Preferably, the groove is formed by bending an end edge portion inward in a zigzag arrangement. With this configuration, a gap continuous along the whole circumference of the joint portion can be formed between a base end piece of the zigzag bent portion and the outer circumferential surface of the outer box and the distance from the outer box to the structural materials can be made longer. Accordingly, at the time of disassembling after scrapping an opposite portion of the outer circumferential surface of the outer box to the base end piece of the zigzag bent portion can be cut easily without keeping cutting depth accurate. Accordingly, air can be introduced inside and the shell can be opened easily, so that respective structural materials can be taken out without damage and collected.
Preferably, the groove has a wide reservoir portion at its upper portion for reserving a liquid substance to prevent it from overflowing from the groove. With this configuration, the shell can be filled with an amount of adhesive agent sufficient to seal and the adhesive agent can be also prevented from overflowing to the outside, so as to improve workability and prevent both staining of a core material with the adhesive agent and adhesion of structural materials to the shell by the adhesive agent.
Preferably, the liquid substance is constituted by an adhesive agent containing particles or powder of a metal oxide or a metal nitride With this configuration, permeation of various kinds of gasses, water vapors, etc. can be suppressed, so that degradation of heat insulating property caused by vacuum loss over time can be prevented.
Preferably, a mark or indicia is provided in the outer circumferential surface of the zigzag bent portion. With this configuration, a portion to be cut without damage of structural materials to be collected can be easily found at the time of disassembly.
According to another aspect of the present invention, a method for producing a full vacuum heat insulation box body includes integrating an inner box and an outer box onto a first shell which is opened in an open bottom surface of the outer box, inserting a first structural material having continuous pores and a triangular section into the inside of a space formed between the inner and outer boxes constituting the first shell through the opening of the first shell, by inserting a bottom side portion of the first structural material ahead, inserting a second structural material having continuous pores and a triangular section into the space through the opening of the first shell by inserting a vertex portion of the second structural material ahead to thereby fill the inside of the room of the first shell, blocking the opening of the first shell with a third structural material having continuous pores and a shape like a flat plate, enclosing the third structural material with a plate member from the outside to seal the joint portion between the plate member and the first shell to thereby form a second shell which is fully closed, and evacuating the second shell. With this method, a heat insulation box body, in which the inside of the shell is kept in a vacuum and its external appearance is never deformed, can be obtained easily.
Preferably, a structural material to be brought into contact with an uneven surface of the shell is first inserted and a triangular sectional structural material having no uneven surface is finally inserted with a vertex portion thereof inserted ahead, so that the room of the first shell is filled with the structural materials. With this configuration, structural materials abut on the shell without any gap, so that tight wall surfaces can be obtained easily.
Preferably, evacuation of the second shell is performed under the condition that the inner and outer boxes and the structural materials put between the inner and outer boxes are not fixed by an adhesive agent, or the like. With this configuration, structural materials can be disposed of easily, so that working efficiency is improved and the adhesive agent which is a cause of lowering of the degree of vacuum in the shell can be eliminated to suppress loss of vacuum.
Preferably, at least one member of the first shell and the plate member for covering the opening of the first shell is bent at the joint portion to form a groove of a predetermined depth, the groove is filled with a liquid substance formed of an adhesive agent containing particles or powder of a metal oxide or a metal nitride, and after the other member is inserted into the groove filled with the liquid substance, the liquid substance is solidified while evacuating the fully closed second shell to thereby perform both joining and sealing at the joint portion. With this configuration, positioning can be made easily and the joint portion can be sealed securely.
According to a further aspect of the present invention, a method for disassembling a full vacuum heat insulation box body having a shell constituted by inner and outer boxes, and structural materials disposed in the shell, the inner and outer boxes and the structural materials being merely fixed by close-contact caused by means of a vacuum includes cutting a surface of the shell to thereby introduce air into the inside of the shell so as to allow the inside state of the shell to return to an atmospheric pressure state, then separating the materials of the shell and the structural materials from each other. With this method, the inner and outer boxes and structural materials can be separated from each other by a simple operation of destroying the vacuum state. Accordingly, respective members can be collected and recycled easily.
Preferably, a joint portion between the inner and outer boxes is constituted by a groove formed by bending an end edge portion of one member of the boxes inward in a zigzag and filled with a liquid substance, and an end side portion formed in the other member of the boxes so as to be able to be inserted into a deep portion of the groove. Also, preferably, cutting of the shell surface is performed by providing a notch in an outer surface of the one member having the zigzag bent portion along a position corresponding to the zigzag bent portion, and the inner and outer boxes are then separated from each other and the materials of the shell and the structural materials are recovered. With this configuration, as the cut portion of the shell is apart from a structural material is so as to have a gap between them, this portion can be cut easily without keeping cutting depth of the notch accurate and the shell can be opened. Accordingly, respective structural materials in the inside of the shell can be taken out, collected and recycled without damage.
Preferably, the outer box has an opening portion used for insertion of structural materials which is closed with a plate member, and a joint portion between the outer box and the plate member constituted by a groove formed by bending an end edge portion of one member of the outer box and the plate member inward in a zigzag and filled with a liquid substance, and an end side portion formed in the other member of them so as to be able to be inserted into a deep portion of the groove. Cutting of the shell surface is performed by providing a notch in an outer circumferential surface of the member having the zigzag bent portion along a position corresponding to the zigzag bent portion, and the outer box and the plate member are then separated from each other and the materials of the shell and the structural materials are recovered. With this configuration, since the cut portion of the shell is separate from a structural material so as to have a gap between them, this portion can be cut easily without keeping cutting depth of the notch accurate, and the shell can be opened. Accordingly, respective structural materials in the inside of the shell can be taken out, collected and recycled easily without damage.